This invention relates to an industrial robot device traveling on a traveling stand, and more particularly to a mounting structure of the traveling stand in which traveling original point can be set with accuracy.
FIG. 1 is a perspective view showing the entire arrangement of an ordinary traveling type industrial robot device. In FIG. 1, reference numeral 1 designates a traveling stand laid on a concrete floor; 2, a traveling type industrial robot device; 3, a traveling motor for driving, in response to an instruction from a control device (not shown), the robot 2 to a predetermined position on the traveling stand 1; 4, guide rails along which the robot device 2 moves linearly; 5, a rack engaged with a pinion (not shown) of the rotary shaft of the motor 3; 6, a pair of limit switches provided at both ends of the traveling stand 1, to prevent the over-running of the robot device 2; and 7, an original-point position detector arranged adjacent to one of the limit switches 6. When a dog 8 provided on the traveling robot device 2 approaches the detector 7, the latter 7 detects it and applies an original point position detection signal to the control device.
FIG. 2 is a plan view showing a plurality of work stations 9, (9a, 9b and 9c) which are arranged on the concrete floor along the traveling stand 1. At the work stations, a welding operation, assembling operation, etc. are carried out by the robot device 2. In FIG. 2, reference numeral 7 designates the aforementioned original point position detector.
With the traveling type robot device thus organized, teaching data on each of the reference positions of the work stations 9 which are determined from the number of revolutions of the pinion engaged with the rack 5 by referring to the position detected by the original point position detector 7 are stored in a memory in the control device (not shown). When robot work is started, the position of the robot device 2 is coincided with the plurality of work stations 9 in a predetermined order, with the original point position as a reference, according to the positions of the work stations stored in memory, so that a variety of robot work such as welding work, assembling work and the like are carried out at the work stations 9.
There occurs such a problem in the above-described conventional traveling type robot device that the expansion and contraction of the traveling stand 1 installed on the concrete floor may not be made constant depending on the degree of tightening of anchor bolts embedded in the floor. This will be described in more detail. The traveling stand 6 is fixed with anchor bolts 10 embedded in the floor at positions A, B and C and with nuts 11 as shown in FIGS. 3A and 3B. The traveling stand is provided with fixing parts, respectively, at the positions A, B and C (hereinafter referred to as "fixing parts A, B and C"). The fixing parts A, B and C have bolt holes 12, each of which has a clearance with the amount of expansion of the traveling stand 1 taken into account as shown in FIG. 3B. Therefore, for instance when the degree of tightening of the bolts at the fixing part A is larger than those at the fixing parts B and C, the positions of the bolt holes 12; that is, the positions of the fixing parts B and C of the traveling stand 1 are shifted against the force of tightening the anchor bolt 10 as much as the amounts of expansion .DELTA.LB and .DELTA.LC at the fixing parts B and C with the fixing part A as reference which amounts of expansion correspond to the linear expansion coefficient of the traveling stand 1.
However, the degree of tightening at the fixing part A is not always larger than those at the fixing parts B and C. If it is decreased because of external vibration or fat and oil stuck, then the fixing part A is shifted with respect to the fixing part B or C as a reference. As a result, the reference distances la, lb and lc of the work stations 9a, 9b and 9c from the original point position detector 7 as shown in FIG. 2 cannot be maintained constant.
In general, if, in a traveling type industrial robot device, its traveling distance is ranged 10 m, the amount of expansion or contraction of the traveling stand 1 is 3 mm or more with the change 30.degree. in ambient temperature. Therefore, if the original point position detector 7 is provided at the end of the traveling stand, then an error 3 mm in maximum is produced between the reference position of the work station 9c farthest from the original point and the reference position of the robot device 2.
The error may be corrected as follows. Temperature correcting means is provided in the control device, and with respect to the traveling distance of the robot device 2 which has been stored at the time of teaching. The number of revolutions of the traveling motor 3 during robot work is corrected as much as the change in temperature which occurs after the teaching. However, when the fixing parts are changed in the degree of tightening as described above, then the distance between the original point and the work stations 9a, 9b and 9c are not constant, and therefore it is impossible to perform the temperature correction accurately.